#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int compare(const void *a, const void *b) {
    return (*(const char*)a - *(const char*)b);
}

int main() {
    char s[1000];
    while (scanf("%s", s) != EOF) {
        int len = strlen(s);
        int m = len / 2;  
        char sp[1000];
        int j = 0;
        qsort(s, m, sizeof(char), compare);
        for (int i = m + (len % 2); i < len; i++) {
            sp[j++] = s[i];
        }
        if (len % 2 == 1) {
            sp[j++] = s[m];
        }
        for (int i = 0; i < m; i++) {
            sp[j++] = s[i];
        }
        
        sp[j] = '\0'; 
        printf("%s\n", sp);
    }
    return 0;
}